In a conventional assessment of environmental impact of manufacture and disposal of a product, some specific steps for manufacturing and disposal are picked up to be assessed by detecting injurious substances and the quantity thereof. It is difficult to employ the above mentioned conventional method to assesses impact on environment precisely when, for example, a very small amount of carbon dioxide is detected in each assessment step in contrast with the large amount of the total carbon dioxide detected from the whole assessment steps. Accordingly, an LCA (Life Cycle Assessment) has been studied, in which environmental impact is assessed quantitatively during processing of manufacture through disposal of a product, as described in report "Present Condition of LCA in Japan and Problems in the Future" 1994 by Ecomaterials Forum.
In a conventional method, the life cycle of a product is divided into some steps arranged in series. It is difficult to assess the impact on the environment of complicated manufacture and disposal of a product, which is composed of a large number of parts, such as electrical and mechanical devices. Usually, each step of the life cycle of a product is not defined clearly; and therefore, it is difficult to assess the impact of manufacture and disposal of a product on the environment precisely.